cpg_initialize man page

The cpg_initialize function is used to initialize a connection to the closed process groups API. This function is deprecated and cpg_model_initialize should be used in newly written code.

Each application may have several connections to the CPG API. Each application uses the handle argument to uniquely identify the connection. The handle argument is then used in other function calls to identify the connection to be used for communication with the CPG service.

Every time an CPG event occurs within the joined group, one of the callbacks specified by the argument callbacks is called. The callback functions are described by the following type definitions:

When a configuration change occurs or a message is to be delivered one of the callbacks is called from the cpg_dispatch() function. If a configuration change occurs, cpg_confchg_fn is called. If a delivery of a message occurs, cpg_deliver_fn is called.

where nodeid is a 32 bit unique node identifier, pid is the process ID of the process that has joined/left the group or sent the message, and reason is an integer code indicating why the node joined/left the group.

CPG_REASON_JOIN - the process joined a group using cpg_join().
CPG_REASON_LEAVE - the process left a group using cpg_leave()
CPG_REASON_NODEDOWN - the process left a group because the node left the cluster.
CPG_REASON_NODEUP - the process joined a group because it was already a member of a group on a node that has just joined the cluster
CPG_REASON_PROCDOWN - the process left a group without calling cpg_leave()